The modern communications era has brought about a tremendous expansion of wireline and wireless networks. Computer networks, television networks, and telephony networks are experiencing an unprecedented technological expansion, fueled by consumer demand. Wireless and mobile networking technologies have addressed related consumer demands, while providing more flexibility and immediacy of information transfer.
Current and future networking technologies continue to facilitate ease of information transfer and convenience to users. Such increased ease of information transfer and convenience to users has recently been accompanied by an increased ability to provide mobile communications at a relatively low cost. Accordingly, mobile communication devices are becoming ubiquitous in the modern world. With the rapid expansion of mobile communications technology, there has been a related rapid expansion in those services that are demanded and provided via mobile communication devices.
Over the history of mobile communications, there have been many different generations of systems developed to enable the use of such communication devices. The first generations of these systems were sometimes developed independently and, at least initially, were not necessarily usable in cooperation with other systems. However, cooperation between communication system developers began to be employed so that new technologies could be enabled to have the potential for synergistic cooperation with other technologies in order to increase overall capacity. Thus, a mobile terminal operable in second generation (e.g., 2G) systems such as GSM (global system for mobile communications) or IS-95, which replaced the first generation of systems, may in some cases be useable in cooperation with newer generation systems such as third generation systems (e.g., 3G) and others that are currently being developed (e.g., E-UTRAN (Evolved Universal Terrestrial Radio Access Network)).
The ability of a particular mobile terminal to access multiple systems or communicate via multiple radio access technologies (multi-RAT) is sometimes referred to as “multi-radio access” (MRA). An MRA capable terminal may therefore be enabled to transfer between different RATs (e.g., UTRAN, E-UTRAN, GERAN (GSM EDGE radio access network)). Under certain circumstances, a mobile terminal (or user equipment (UE)) may perform cell reselection in order to transfer between different RATs. In this regard, for example, due to signal loss or signal strength reduction in a current serving cell, the UE may reselect another cell. Various procedures governing cell reselection have been developed to try to maintain communication continuity and provide for selection of the best available cell (regardless of RAT) in a multi-RAT environment.
The Third Generation Partnership Project (3GPP) has specified reselection procedures in various technical specifications (TSs). For example, 3GPP TS 25.304 provides cell reselection procedures for UTRAN. These procedures account for the fact that existing equipment in the field may have different ages and/or capabilities based on the upgrades that have been incorporated therein. As such, for example, a priority based cell reselection algorithm was introduced to use absolute priorities to make cell reselection choices in connection with 3GPP Release-8 (Rel-8) networks, while Rel-7 and older previously deployed networks that are not upgraded to support the priority based cell reselection algorithm may instead use a legacy algorithm for cell reselection that is based on cell ranking instead of cell priority.
When reselecting to a target RAT that does not support the priority based algorithm, existing methods have taken the view that reselection towards such a RAT should also be based on cell ranking. As such, “symmetric” reselection rules would be applied between both RATs. In order to achieve this behavior, if a UE in UTRAN has received no priority information for any frequency of a target RAT in a selected public land mobile network (PLMN), the UE uses the legacy cell reselection algorithm towards the RAT that does not support priority based cell reselection. However, when the serving network interworks with two or more other networks, this could lead to scenarios where the priority algorithm and the legacy algorithm are running within the UE in parallel, thereby causing excessive complexity in the UE. Moreover, some alternatives to the running of parallel algorithms may lead to situations in which reselection of RATs that do not support priority based reselection may be completely disabled and thus particular RATs may effectively be disabled from being selected. Accordingly, changes to the procedures for inter-RAT cell reselection may be desirable.